The present invention relates to a clamping arrangement for hollow objects and, more particularly, hollow cores for winding newsprint and the like. Newsprint rolls and the like are wound on hollow cores, and are characterized by large mass and inertia. For example, rolls of newsprint may be approximately 1.40 meter long with a diameter of approximately 1.00 meter and have a mass in excess of 1,000 kg. During winding and unwinding operations of newsprint rolls and the like, and particularly when these operations are abruptly halted during emergency situations, large forces and torques are applied to the hollow cores with small inside diameters, typically on the order of 7.5 centimeter.
Various types of clamping arrangements for hollow cores are known. However these known arrangements have shortcomings relating to time consuming procedures for preparing the hollow core for the clamping action, the incompatibility with robotic handling procedures, the poor load transfer between the hollow object and the clamping arrangement, the damage inflicted on the hollow core, the inability to adjust to the core inside diameter, the inability to release the hollow core upon removal of the clamping force, and to the complexity and inherent production cost of the clamping arrangement.
Shafts are known which can be slid, usually in a fairly complicated manner, through the hollow cores and which are combined with elements which can spread out from the shaft to hold the core on the shaft. Such shafts require operation by at least two persons when handling heavy rolls. Due to the high labor cost associated with this time consuming procedure, shafts of this type are no longer considered for high production printing facilities.
Increased production demands on printing facilities have led to the development of mobile robots that retrieve a newsprint roll from a storage facility and load this roll on the printing press. Current robotic systems are incompatible with clamping arrangements that are based on a preferred orientation of the newsprint roll, such as arrangements that use a keyway in the hollow core, and with clamping arrangements that are incapable of releasing the empty core that remains after unwinding of the web material to prepare the printing press for loading of another roll, such as arrangements that depend on metal caps on hollow cores for the transmission of torque from the clamping arrangement to the hollow core.
Clamping arrangements are known which employ a cone tapering from a diameter slightly larger than the hollow core's inner diameter to a diameter slightly smaller than the hollow core's inner diameter. In this arrangement the V-shaped grooves placed on the circumference of the cone facilitate the torque transfer from the clamping arrangement to the hollow core and vice versa. These cones have the tendency to damage the ends of the cores and therefore do not provide for reliable transfer of high torque loads to the cores. Furthermore, (during continued rotational acceleration and deceleration of the hollow core the damage inflicted on the hollow core increases which leads to a further degradation of the ability of the clamping arrangement to transfer high torque loads. In some cases, hollow cores are equipped with metal end-caps to overcome the poor load transfer between the clamping arrangement and the hollow core. However, use of the metal end-caps causes excessive wear to the clamping arrangement during normal operation and in practice it is difficult to ensure a reliable load transfer between the metal cap and the hollow core. Frequently metal caps make insufficient contact with the hollow core and occasionally cause combustion of the web type material induced by the rapid spinning of the metal cap with respect to the hollow core. Use of the metal end-caps has the added disadvantages that they increase the cost of newsprint and that they prohibit recycling of the core and the newsprint that remain at the completion of the unwinding operation.
Clamping arrangements are known comprising of a plurality of jaws which can spread by being swingably mounted on pivots, or by moving the jaws along conical or cylindrical surfaces in axial direction. Known clamping arrangements in these categories incorporate a large number of parts and are characterized by large rotations or translations of the jaws during the clamping motion, which are therefore prone to considerable wear during normal operations. Due to these shortcomings, known clamping arrangements in these categories are expensive to produce and have high maintenance costs. Jaws swingably mounted on pivots have the added disadvantage that the clamping force is transferred through the pivots which are ill suited for this purpose, and that, to facilitate the pivots, the integrity of the jaws themselves must be compromised. Clamping arrangements involving jaws that are moved along conical surfaces in axial direction have the added disadvantage that these clamping arrangements are longer than their counterparts and often cannot be placed in the limited space available between the hollow core and the mount for the clamping arrangement. Clamping arrangements involving jaws that are moved along cylindrical surfaces in the axial direction have the added disadvantage that they are incapable of clamping hollow objects of larger dimension than the center portion of the clamping arrangement and that the clamping pressure exerted by the clamping arrangements on hollow objects cannot be adjusted.
Dual acting clamping arrangements are known in which the longitudinal and radial clamping of the hollow core is achieved through two or more separately controlled mechanisms incorporated in a single clamping arrangement. Although dual acting clamping arrangements offer superior clamping performance, they dramatically increase the cost of peripheral equipment that accommodate separate control of the two mechanisms incorporated in the clamping arrangement. In most newsprint winding and unwinding facilities only the longitudinal movement of the clamping arrangement can be controlled, making the use of dual acting clamping arrangements infeasible.